1. Field
The present disclosure relates to a cement that bonds casing to a wellbore. More specifically, the present disclosure relates to a cement that bonds casing to a wellbore, and that includes cross-linked polymers.
2. Related Art
Hydrocarbons that are produced from subterranean formations typically flow from the formations to surface via wellbores drilled from surface that intersect the formations. Most wellbores are lined with casing and strings of production tubing inserted within the casing that are for conveying the hydrocarbons to surface. The casing is usually bonded to the inner surface of the wellbore with a cement that is injected into an annulus that is between the casing and wellbore. In addition to anchoring the casing within the wellbore, the cement also isolates adjacent zones within the formation from one another. Without the cement isolating these adjacent zones fluids from the different zones, which are sometimes different, could become mixed in the annular space between the casing and wellbore wall. When one of the different fluids is water, separating it from the hydrocarbon is required. Further, if the water producing zone is at a pressure exceeding that of a hydrocarbon producing zone, water sometimes migrates into the hydrocarbon producing zone to thereby reduce the hydrocarbon producing potential of the wellbore.
The cement also prevents hydrocarbon fluid from flowing uphole from a hydrocarbon producing zone to the surface and in the annulus between the casing and the wellbore wall. Without the cement, or in instances when cement has failed, hydrocarbons are known to migrate to surface and then present a safety hazard to operations personnel. One problematic area for gas migration exists for deep wells, where fluid densities often as high as 22 pounds per gallon are used to control gas or formation fluid influx. To control gas migration, cement densities for successfully cementing of the zone of interest are sometimes as high as 22.7 pounds per gallon. As a cement slurry sets, hydrostatic pressure is reduced on the formation. During this transition, reservoir gases can travel up through the cement column resulting in gas being present at the surface. The permeable channels from which the gas flows cause operational and safety problems at the well site. Causes of gas channeling include: (1) bad mud/spacer/cement design that allows passage of water and gas resulting in failures in cementing operations; (2) high fluid loss from cement slurries, which causes water accumulation and results in micro-fractures within the cement body; and (3) cements not providing sufficient hydrostatic pressure to control the high pressure formation.